A method was developed to measure the rate of incorporation of palmitate from plasma into different brain regions in the awake rat, Jpalm. Furthermore, a theoretical model was developed to calculate Jpalm from data, and to interpret the results. Jpalm did not change with aging in Fischer-344 rats between 3 and 34 months of age, indicating that the rate of turnover of palmitate-containing brain lipids was unchanged. During development of the rat, Jpalm increased between 15 and 20 days, then fell more than 8 fold to maturity. The time course corresponded to the time course of myelination in the developing brain. Jpalm was found to fall in the pituitary and pineal glands of Brattleboro rats as compared to controls, and to fall in central auditory pathways following damage to the cochlea of rats.